‘-q’ ‘--quiet’ Turn off Wget's output. ‘-nv’ ‘--no-verbose’ Turn off verbose without being completely quiet (use ‘-q’ for that), which means that error messages and basic information still get printed.
So there is no way to just get error messages. Wait. Google says: "To display only error messages from wget and suppress all other output, including progress indicators and successful download messages, use the -nv (no verbose) option in conjunction with redirection of standard output to /dev/null." I see. Well please mention that in the manual.